The present invention relates generally to automatic screw machines, and more particularly, to a system for adapting screw machines into computer numeric control ("CNC") operated machines by incorporating a unique VersaCam device in place of a conventional hard cam.
Conventional automatic screw machines have been known for some time. These machines have a high capability for producing a large number of identical parts. When small quantities are required, however, the time and expense to produce the special control cams necessary for operation of the machine, makes the use of a conventional automatic screw machine less desirable.
One of the operational functions of the screw machine is the movement of the machine tool relative to the work piece, which is generally accomplished by longitudinal movement of a tool turret and lateral movement of two or more cross slides. At least two cross slides are usually provided on a conventional screw machine. The cross slides typically move lateral to the spindle of the machine. Other cross slides may be positioned at specified angles relative to the basic cross slides.
Other functions important to the machine include the indexing of the toot turret, the feedout of the stock, and the control of the spindle speeds. In conventional, single-spindle automatic screw machines, the timed sequence of the above functions is controlled mechanically through cams, trip dogs, trip levers and cam followers, which result in the engagement of the conventional machine mechanisms through clutches, gears, and similar devices at the proper time. Such an arrangement of mechanical devices is found in any conventional automatic screw machine.
A cam made for one job can often be used on other jobs, although any change in machine speed or feed rate in any part of the sequence will result in slowing down the entire job. The alternative is to make a complete new set of cams specifically designed for the new job. For these and other known reasons it is desirable that some or all of the operations of the automatic screw machine be controlled by a numeric control system. With a numerical control system, the machine functions can be controlled through electrical signals by a software program, and the requirements of each job can be programmed into the apparatus. There are newly made automatic screw machines which have this numerical control capability. However, there are a vast number of existing automatic screw machines of the conventional variety which do not have this capability. Therefore, a system for retrofitting these conventional machines is needed.
Accordingly, a system for retrofitting a conventional automatic screw machine to accept numerical control is provided by the present invention. The present invention may also be incorporated into newly manufactured screw machines that do not have CNC capability. A conventional automatic screw machine includes a plurality of mechanical timing means which operate through engaging means, such as clutches and gears, to connect a main driving means to various operating mechanisms of the machine. These mechanisms control the individual functions of the machine, for example, spindle speed, the indexing of the tool turret and the feeding of stock through the spindle. Also, the movement of the turret slide, towards and away from the work piece, and the movement of the cross slides are controlled through cam means usually including a cam and a camshaft, which are driven by drive shaft means which in turn is driven by the main driving means.
The VersaCam system of the present invention is a versatile replacement for the turret cam of a single-spindle screw machine. The VersaCam can drive the cam follower so as to mimic any possible cam profile. The VersaCam is a CNC machine with a mechanical output that displaces the cam follower of a cam-logic machine. It comprises a mechanism to drive a cam follower, an actuator to power this mechanism, a sensor to determine the position of the mechanism, a control system which causes the mechanism to follow a desired trajectory (as a function of cam drive shaft position), a means for specifying desired trajectory, and a sensor to determine the position of the cam drive shaft.
The VersaCam system of the present invention is not designed to replace the mechanical timing of conventional machines but rather will use and work with the mechanical timing found in conventional machines. Further, the VersaCam system does not require disconnecting the cross slides, but uses them as they are normally used in the operation of conventional machines. The VersaCam system depends on the position of the driving camshaft for its operation. The VersaCam system uses an electric drive and is designed to drive the turret without modification to the turret.
In another embodiment of the present invention the screw machine turret slide may be actuated directly, rather than through the cam follower. A linear actuator may be provided, in direct contact with the turret slide, which actuator may be hydraulic, ball-screw based, or of other common hardware.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following descriptions of the drawings and preferred embodiments.